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Transcript
Can you guess why I am showing you this picture? Electromagnetic Waves, Stars, and The Universe Contents: • How we know what’s in a star (emission spectra) • Nuclear Fusion • Star life cycles (our sun versus massive stars) • Supernovae and creation of heavy elements • Black Holes • Big Bang Theory, with Evidence Longer wavelengths (left side) have less energy. Think of these waves a 1. Which type strings that areofbeing shaken. Rapidly shaken (high energy) strings look like electromagnetic radiation is the ones on the right. typically most dangerous? 3. What color are the Why? hottest stars that we can see? The coolest stars? Gamma rays. Shorter wavelengths have more energy. Blue. Red. 2. Under the right conditions, even visible light can be dangerous. Can you describe one such condition? Laser light. When visible light is amplified and brought “into phase,” it can become intense enough to burn things. These shorter wavelengths have more energy. That’s why they’re dangerous. The Electromagnetic Spectrum •Visible light is just a small segment of the continuum. •The “red end” of the spectrum has longer wavelengths. The “blue end” has shorter wavelengths. •Shorter wavelengths have higher energy, so we know that a red star is cooler and a blue star is hotter. Blue stars – 40,000 degrees These green stars are bogus! The stars in the middle of the “rainbow” actually look white, because they’re a mix of the colors on either side. When you mix all the colors of light, you get white. Red stars – 3,000 degrees 4. Why are there no green stars? If a star’s radiation output Why there are is centered on green, that no green star produces all colors of stars… the spectrum. A star that produces every color will appear white. •Stars emit many different wavelengths of “light.” •Light refracts (turns) when it passes through materials of different density (such as a glass prsim. 5. Which color refracts the different so a most?amounts, Least? •Different wavelengths refract prism can separate light into a color spectrum. Blue. Red. Correct Refraction Incorrect Refraction,but it shows light from a star. A spectroscope separates radiation into its component wavelengths in an organized way that can be easily analyzed. •When elements are in gas state, they absorb or emit specific wavelengths of radiation. •The wavelengths of radiation an element emit or absorb depend on their electron configurations. •Those wavelengths can be used as a “fingerprint” to identify elements in distant stars. 6. In the diagram, whichabsorb light, their 7. Why do different •When gases electrons orbit faster, part shows emission of elements absorb and emit causing them to jump out to more distant energy levels light? Which part shows different colors? (orbiting farther from the nucleus). absorption of light? •When electrons release energy (by giving off light), they Each element has a themdifferent to fall arrangement inward to of an orbit The bottom diagram, “deslow shows down. This causes excitation,” emission (giving off) of light. closer to the nucleus. The top diagram, “excitation,” shows absorption of light. electrons. Some electrons fall farther, giving off light with more energy (and a different color). “Fingerprints” of different elements Are these absorption spectra or emission spectra? Emission Example •The black lines are wavelengths of radiation that are absorbed by Neon. •If we see these black lines when we analyze starlight with a spectroscope, we know that neon is in the star. Neon Absorption Spectra In the sun, nuclei fuse. When they do this, the products of fusion have less mass than the nuclei that fused. This “lost” mass is actually converted to energy, according to Einstein’s famous equation… E = Energy produced by nuclear fusion C = Speed of light M = Mass that’s “lost” when nuclei fuse. In average 9.an Why will thestar, sunlike getour sun, most its energy bigger as of it gets older? comes from the fusion of Fusion produces helium Hydrogen. Hydrogen (heavier than Hydrogen), produces helium when it which sinks to the sun’s fuses. core and displaces This heliumoutward. is heavier, so it hydrogen sinks to the sun’s core and 10. Whythe willhydrogen the sun turn pushes redder as it gets older? outward. As ages, this outward Asour thesun fusing hydrogen movement of fusing moves outward, it Hydrogen willless cause the sun encounters pressure, to soexpand. fusion slows down. Temperature drops. This outward movement also causes the rate of hydrogen fusion to diminish (due to lower pressure away from the core), thus cooling the sun. Cooling will turn it red. 11. AfterAtour sun point, burns fusion up all of whysun’s core. The sun some willitsnousable longerhydrogen, occur in the will it shrink? will cool, and that cooling will cause it to shrink. This shrinkage will whichshrink will, in turn,they cause the sun to heat back It will coolcreate down.compression, Things generally when cool up (and turn from a cooler red to a hotter white). This stage is down. called a white dwarf. 12. Shrinking will cause the sun to turn white (becoming a white dwarf). Why? As the sun shrinks, it will compress itself. This will cause it to heat back up and turn from red to white. 13. Eventually, our sun will turn into a black dwarf. Why? The compression that heats up a white dwarf is the last energy source for the sun. After this energy is radiated into space, there will be no more. The sun will become cold and dark. This stage is called a “planetary nebula.” The super hot core creates a “solar wind” that blasts away and “lights up” the outer layer of gases. With no fuel remaining, the star will eventually radiate its heat into space and turn to a cold, dark “black dwarf.” In the beginning, the massive star on the right was mostly _________. Hydrogen In a massive star, there is enough pressure to layers cause of a massive star come from? Where do the inner more fusion. Simply the elements Fusion put, of the outer layersin the inner layers come from fusion of the elements in the Why does the “ash” that is created by fusion move to the outer layers. It all starts with center of the sun? hydrogen fusion… When atoms fuse, their product is a heavier, denser The fusion process continues material. Denser materials sink. until iron is created. Even in a massive star there is not enough pressure for iron nuclei to fuse. Lifea massive Cycle of massive star (25 times size of thematerial sun) When stararuns out of fuel, it collapses. Thethe collapsing outer 16. Immediately after running out of fuel, a massive star’s speeds toward the star’s center at an extremely high velocity. This outer material temperature will ________. then slams into the core and “bounces” back outward. This bounce is an explosion Decrease called a supernova. 17. The temperature change of #16 will cause the volume of the star to ________. shrink 18. When a massive star runs out of fuel and collapses on itself, its mass collides at its core and bounces back in an explosion called a ____________. As a result of this explosion, the outside layers of the massive star fly away into space, where they can form _____________. If the mass remaining in the dead star’s core is 3 times our sun’s mass, it will form a ____________. If it is less, a __________ may form. supernova New nebulas that can turn into new solar systems like ours Black Hole Neutron Star Click mouse for questions 16-18 Life Cycle of a massive star (25that times theeven sizeheavier of thethan sun) A supernova produces such high pressures elements iron are formed by were fusion. of these elements are scattered into space and 18.5 Where theMany heaviest (heavier than iron) “recycled.” They new nebulas that create new stars. elements in our form bodies created? Supernova explosions Scientists believe that all of the earth’s heavy elements were created in a massive star ago. from dying stars sometimes 19.that Whyexploded does thelong material form “neutron stars?” Our solar system formed shrink There is so like much that the positive protons and from a nebula thispressure one, the negative electrons fuse to become neutrons. but smaller. 20. Two characteristics of Neutron stars are: Extreme density (3 suns compressed into the size of a city --one spoonful would have the same mass as all of the cars on the earth) and very rapid spinning. Scientists believe the heavy elements in our solar system came from a supernova. Lifeouter Cycle of aofmassive The portions the star arestar blasted outward and scattered through space. (25 times the size of the sun) Ultimate Fate of A Massive Star (Greater than 25 Solar masses) The core becomes so compressed that protons (+) and electrons (-) fuse to create neutrons… If the material remaining in the core is less than 3 solar masses, a very dense “neutron star” is created. If the material remaining in the core is greater than 3 solar masses, its gravitational force is strong enough to cause the collapse of neutrons. The mass compresses itself into an infinitely small point whose gravity is so intense that not even light can escape from it. Our Sun is an average star like this one. The “Singularity” The “Event Horizon” The Big Bang Theory suggests that the universe exploded outward from an infinitely small point, called the “cosmic singularity” – and that the universe has been expanding ever since. Evidence supporting the Big Bang Theory: 1) Microwave Radiation: Space is filled with low-energy microwave radiation of same temperature that scientists predicted would be left over from the Big Bang. More Big Bang Evidence: The Doppler Effect •Waves emitted by a moving object are compressed in front of the object and stretched out behind the object. •When a star moves toward us, we see shortened wavelengths. This is called a “blue shift,” because the blue end of the light spectrum has shorter wavelengths. 2) All distant galaxies, and most nearby galaxies, have redshifts (stretched waves), indicating that they are moving away from us, and that, therefore, the universe is expanding.